Unmanned aerial vehicles, or drones, could soon be patrolling the United States border with Mexico 24 hours a day, seven days a week. That's what the major immigration reform bill introduced last week by a bipartisan group of senators proposes.

The goal: "effective control" of the border. Under the bill, no immigrant granted provisional legal status would be eligible to apply for a Green Card until the Department of Homeland Security shows it's made substantial progress toward that goal. Border hawks want the pathway to citizenship more firmly tied to border security success.

Ten Predator B drones already patrol the nation's borders. Some worry authorities will use drones to spy on Americans without due process.

San Diego-based General Atomics provides Predator drones to the DHS and the U.S. military.

Several weeks ago, the anti-war group Code Pink protested in front of the home of General Atomics CEO Neal Blue. They launched a baby drone that was soon confiscated by a police officer.

"It's my drone and I want to know why I can't fly it over Neal Blue's house," Code Pink co-founder Medea Benjamin said to the officer.

Up until now, 36-foot-long Predator drones have been used on the southern border to patrol remote areas of Texas and Arizona.

They've also been lent out to other federal agencies like FEMA, which used the drones to survey flood damage.

"UAVs provide real time intelligence and information as well as providing officer safety," Cuellar said.

The drone caucus, as it's also known, advocates for increased use of unmanned aerial vehicles, or UAVs, for national security, military and law enforcement operations.

Cuellar does say, however, that we need more information about the work of the border drones.

"We gotta have efficiencies, effectiveness, accountability on how they're used," he said. "But again, keep in mind, look at the history how they've been used extremely well in the military."

Of course, military drones are best known as stealth killing machines, while the border drones are used strictly for surveillance.

Thus far the only statistics that border authorities have released to the public reveal pretty mediocre results.

After more than 5,700 hours of flying time last year — at a total operating cost of at least $18 million — drones helped agents confiscate just three percent of all drugs seized along the border last year.

Information recently uncovered by the California-based Center for Investigative Reporting suggests there are many, many more illegal crossers who got away. CBP reports obtained by the center suggest fewer than half of the illegal border crossers detected by a drone were arrested.

"It's one thing to have data coming from a drone; It's another thing to be able to respond to it," said David Shirk, an expert on border security at the University of San Diego.

Catching illegal crossers spotted by drones would require agents on the ground in the remote areas where drones currently patrol. The senators' bill could address this: it calls for adding 3,500 new CBP officers to its current staff of more than 60,000.

And the extra billions earmarked in the bill for a new border security strategy could help authorities tackle at least some of the other problems with the border drone program.

Problems like getting them up in the air. Last May, Homeland Security's Inspector General reported that the border drones were on the ground 70 percent of the time they were supposed to be flying. Bad weather was one excuse, but the Inspector General also cited management problems and a lack of qualified staff and equipment.

David Shirk said he thinks more drones patrolling the border would be effective in revealing smuggling patterns.

"(But) the real question is, number one, will we be able to use the information we get from drones effectively to address the problem? And two, what's the cost-benefit?" he said.

CBP has never released such an analysis publicly. And some security experts wonder if there could there be other types of drones or technology that could better provide that Holy Grail of effective border control.

Maybe. But right now, CBP is already locked into a nearly half-billion dollar contract with San Diego's General Atomics. The contract covers maintenance and equipment for the existing fleet, and up to 14 new drones.

Click below for more from Fronteras:

Read more from the public media collaboration Fronteras: The Changing America Desk at fronterasdesk.org.